This invention relates to a gas turbine having blades each being designed to be cooled from the inside by a cooling medium, and also relates to improvement in such a blade.
Recently, in order to enhance the performance of a gas turbine engine, the temperature of the combustion gas has been raised higher, so that blades of the gas turbine operate in a very thermally severe environment.
Therefore, these blades should be sufficiently cooled by some cooling means.
Generally, for cooling a turbine blade of this type, there has been extensively used a method in which part of the compressed air used for combustion purposes is caused to flow through a cavity portion within the blade. A typical example of such a blade cooling method is disclosed, for example, in Japanese Patent Unexamined Publication No. 2-241902.
With respect to the shape or profile of a blade of this type, a camber line constituting a central factor in the blade profile shape is defined by a circular arc, part of a parabola, or part of another smoothly-changing curve, and the blade profile is determined or designed along this camber line. In this case, the thickness of the blade first increases progressively from a leading edge thereof toward a trailing edge thereof to reach a maximum value, and then decreases progressively to the trailing edge.
The gas turbine blade thus formed is cooled from its inside, as described above. In the case of the gas turbine, the air used for this cooling operation is usually provided by a part of the combustion air. Therefore, when the amount of consumption of the cooling air is large, the combustion air is limited, which affects the operation cycle of the gas turbine to be operated under the high temperature. Therefore, it is desirable that the amount of the cooling air used for cooling the blades be minimized.